Atlantic Council: The United States and its allies must be ready to deter a two-front war and nuclear attacks in East Asia

Introduction

“If hostilities were to renew on the [Korean Peninsula] it is not a matter of ‘if’ the Chinese Communist Party will intervene, it is when … This has been a very difficult topic for us to address as an alliance.”— Retired Gen. Robert Abrams, former commander of US Forces Korea (USFK)¹

“I’ve wargamed conflicts with China and with North Korea dozens of times. If we look at a map and consider the forces involved, it is almost impossible for either to occur without some form of simultaneity.”—US defense official, name withheld

“If the political survival of Xi Jinping or Kim Jong Un is at stake in [a] military conflict they are losing, escalating to a limited nuclear strike would be rational … hesitating to use nuclear weapons would be the irrational act.”—US intelligence official, name withheld

The challenges to deterrence in East Asia have begun to change fundamentally in recent years, putting them on track to present grave risks to US national security interests over the coming decade. This report summarizes the results of a study focused on two of these emerging and interrelated challenges to deterrence in East Asia. The first is the potential for a conflict with either the People’s Republic of China (PRC) or North Korea to escalate horizontally and become a simultaneous conflict with both. The other is the possibility that either or both adversaries would choose to escalate vertically to a limited nuclear attack—rather than concede defeat—in a major conflict.

US thinking about war in East Asia often neglects the possibility that the United States would have to fight the PRC and North Korea simultaneously rather than separately. Furthermore, conventional wisdom in the United States underestimates the risk that either the PRC or North Korea would resort to a limited nuclear strike in the event of a conflict in the region. However, the recent behavior of the United States’ adversaries in East Asia suggests that this thinking may be off the mark; the PRC military has reorganized itself to prepare to fight a two-front war, while both the PRC and North Korea continue to develop the sophistication and size of their tactical nuclear arsenals.

To better understand the threats posed by these two major risks five to ten years from now (in the 2027-2032 timeframe), we conducted a series of workshops and interviews with key government personnel and experts, and analyzed our findings in this report, originally written for the US Defense Threat Reduction Agency (but not necessarily representing its views). These findings should serve as a wake-up call: The United States and its allies can no longer think about conflicts with the PRC and North Korea in isolation from each other, and they must take urgent action to prepare for the possibility of facing limited nuclear attacks in an East Asia conflict scenario.

Key findings

If a conflict with one adversary in East Asia doesn’t end quickly, expect it to widen. If a conflict is initiated by either the PRC or North Korea, the potential for expansion to simultaneous conflicts with both would pose a high risk to US and allied defense objectives, particularly because this would impose severe operational and strategic challenges. During this study, we found many plausible pathways from which a conflict with one could expand into conflicts with both, even without Beijing and Pyongyang coordinating with one another. Though it is ill-advised to confidently predict the flow of a conflict up to a decade from now, such pathways are sufficiently numerous and plausible that—if a conflict with either the PRC or North Korea does not conclude quickly—we should anticipate that simultaneous conflicts with both could result.

• Deep distrust currently exists between the PRC and North Korea, and we found that neither is likely to feel compelled by any obligation to fight alongside the other—but this would not prevent the emergence of simultaneous conflicts with both. Advance coordination between the two is one of the less likely ways such simultaneous conflicts could emerge. We identified a series of far more plausible pathways, depicted in Figures 1 and 2.
• Simultaneous conflicts impose challenges so severe that the risk should still be considered high, even if the probability of these two conflicts occurring simultaneously is uncertain. The logistical challenges alone are daunting, given the requirements of such major conflicts, including stocks of precision standoff munitions and missile-defense interceptors. Operationally, simultaneous conflicts would force overstretched US command-and-control (C2) systems to make hard choices about how to allocate limited numbers of their most valuable assets. Meanwhile, alliance management and escalation management would become exponentially more complex.
• If North Korean aggression triggers a successful counteroffensive by the US and South Korea, this will likely prompt the PRC to intervene to protect its interests as North Korea collapses. Such intervention would likely spark a confrontation in the context of US-PRC rivalry and distrust, which could escalate to military conflict. Further, Beijing would likely be willing to risk a conflict to prevent Seoul and Washington from dictating the terms of Korean unification via an unchecked counteroffensive.
• Any major US-PRC conflict—for example, if the PRC attacks Taiwan—is likely to escalate horizontally and engulf Korea, unless the US-PRC conflict is a limited war with a quick, decisive outcome. In such a conflict, Beijing is likely to strike US regional bases, possibly including US Forces Korea (USFK) bases well within mutual striking distance of the PRC mainland. Even if the South Korean military and USFK are initially fenced off from hostilities, either side could view them as a US tool to break a stalemate or be drawn in as the PRC attacks US bases in Japan by overflying Korea. Additionally, Beijing could encourage Pyongyang to escalate in order to tie down US and ROK forces. Whether or not Beijing does, a US-PRC conflict would disturb North Korea’s escalation calculus. US reinforcements flowing to the region, along with US commitments and losses, could prompt opportunistic or preemptive aggression from North Korea—particularly because the conflict’s outcome would have immense implications for Pyongyang.
• A second conflict need not even escalate very far for such challenges to come into play. As a major conflict with the PRC or North Korea begins, the potential for escalation to draw in the other immediately affects the political and military options available to the United States and its allies, even if war is averted. Seoul’s efforts to avoid being dragged into a US-PRC war, for example, could constrain US forces in South Korea. Meanwhile, US and South Korean efforts to avoid a war with the PRC could hamstring US-South Korean operations in the Yellow Sea, or in mountainous areas near the PRC-North Korean border.

The risk that a war in East Asia would go nuclear is rising, as the PRC and North Korea have increasing incentive and capabilities for limited nuclear attacks. The risk of a limited nuclear attack by the PRC or North Korea in the event of conflict is likely to grow through the 2027–2032 time frame, and simultaneous conflicts would exacerbate this risk. Building on the results of another study we conducted but have not made public, “Preventing Strategic Deterrence Failure on the Korean Peninsula,” this study found that North Korea has been rapidly advancing its capability and intent to initiate a limited nuclear attack in the event of conflict.³ Though the study did not find evidence as compelling to show that the PRC is currently moving aggressively in this direction, it found evidence that the PRC’s capability to employ nuclear weapons for operational and tactical purposes is increasing.

• North Korean weapons capabilities and policy have moved rapidly toward enabling limited nuclear attacks. Pyongyang’s September 8, 2022, nuclear policy declaration set the stage and justification for limited nuclear attacks, stating that nuclear first use is an option to retake the initiative in a conflict, for example.⁴ Meanwhile, since January 2021, North Korea has been sounding a drumbeat on its tactical nuclear capabilities, including tests of claimed tactical nuclear-capable missiles and displays of a new tactical nuclear warhead.^{5 6}
• Though Beijing may not be matching Pyongyang’s focus on tactical nuclear options, PRC capabilities suited to limited nuclear attack—such as the DF-26 ballistic missile, dubbed the “carrier killer” or “Guam killer”—are already significant and on track to increase.⁷ Though North Korea seems more likely than the PRC to initiate a limited nuclear attack, a North Korean nuclear attack would also raise the risk of a US-PRC nuclear confrontation, particularly if Beijing perceives the US response as threatening. In addition, if a US-PRC conflict starting elsewhere “horizontally” escalates to Korea, and yet PRC victory remains elusive, a “vertical” escalation to limited nuclear attack may be the next logical step from Beijing’s perspective.⁸
• A PRC military intervention in a Korean conflict would also add dangerous new variables to North Korea’s nuclear calculus. An intervention without the North Korean regime’s prompting or permission would be a clear threat to its survival, likely making a limited nuclear attack appear to be the “least bad” option. Conversely, a PRC intervention permitted by North Korea, designed to help protect the regime from the consequences of its escalation, might lead Pyongyang to expect US restraint in response to a limited nuclear attack because of Washington’s fear of triggering a US-PRC nuclear war.

The United States and its allies are not situated to fight a two-front limited nuclear war in East Asia; the PRC may be soon. US and allied capabilities, command-and-control arrangements, and posture (including forces, bases, and agreements with allies) are unsuited to prevent simultaneous conflict with the PRC and North Korea and/or a limited nuclear attack or provide robust military response options if they occur.

• Based on the workshop discussions, the logistical, command and control, basing, and alliance policy considerations of the United States and its allies in the Indo-Pacific all appear designed around and suited for one fight or the other. They aren’t designed for simultaneous conflicts with the PRC and North Korea. Further, this design signals, perhaps unintentionally, that the United States and its key East Asian allies are not yet seriously considering, much less preparing for, simultaneous conflicts. The US-South Korean alliance, in particular, often appears to be avoiding even discussion of this politically sensitive, yet critical, topic.
• The United States and its allies have appeared reluctant in recent years to actively and openly prepare a response to limited tactical nuclear attack in East Asia, much less to prepare to fight a “limited” nuclear conflict. Statements such “a nuclear war cannot be won and must never be fought” and “there is no scenario in which the Kim regime could employ nuclear weapons and survive” may be unintentionally signaling that the United States is deliberately unprepared for such possibilities, and is instead counting on the implicit threat of all-out nuclear conflict resulting from a single nuclear strike as a deterrent.⁹ Decisions and statements about posture and capabilities also signal a disinterest in preparing limited-nuclear-response options, with US officials publicly dismissing the idea of redeploying tactical nuclear weapons to the region.¹⁰
• If current trends continue, the PRC is likely to be far better prepared than the United States to fight on multiple fronts in East Asia and to conduct limited nuclear strikes. The apparent lack of preparedness of the United States and its allies to fight simultaneous conflicts with the PRC and North Korea and for a limited nuclear conflict increases the chances that Beijing or Pyongyang—if already in conflict with the United States—would see advantage in moving first to expand to a dual conflict or escalate to a limited nuclear attack. The PRC’s establishment of a separate Northern Theater Command for Korea contingencies and the Eastern Theater Command for Taiwan contingencies, along with the fielding of accurate dual-capable missiles (nuclear and conventional) shows Beijing’s progress in this direction.

If conflict breaks out, however, the United States has options to manage escalation. The study found that, even if the United States fails to deter aggression by either the PRC or North Korea, there will still be key opportunities for integrated deterrence approaches to help reduce the risk of escalation to conflicts with both, or to a limited nuclear attack. The study identified a range of leverage points in Beijing and Pyongyang’s decision-making that could help to limit such “horizontal” and “vertical” escalation.

• Beijing’s view: Beijing probably wants to limit conflict and avoid a regional or nuclear war if it is employing force to achieve goals regarding Taiwan or maritime disputes, or if it is intervening to protect its interests in a Korea conflict. Workshop participants noted likely concerns in Beijing about the potential for uncontrolled escalation in such scenarios, and one expert particularly highlighted that Beijing’s “nightmare scenario” could be fighting the United States, Japan, and South Korea simultaneously. Given the difficulty that Beijing has had in influencing or constraining Pyongyang under more stable circumstances, PRC leaders are likely to believe that expanding a US-PRC war to the Korean peninsula would introduce new, uncontrolled, and unpredictable elements and complicate conflict termination. Similarly, Beijing likely recognizes that a military intervention during a North Korean conflict with South Korea and the United States holds many risks and uncertainties, including unpredictable effects on Pyongyang’s escalation calculus.
• Pyongyang’s view: Though North Korea is likely to see both opportunities and threats in the event of a US-PRC conflict, it almost certainly would be initially hesitant to embark on a level of aggression risking regime-ending consequences. Pyongyang would likely be skeptical of Beijing’s willingness to prioritize defending North Korea, even as “co-belligerents” fighting the United States and its allies simultaneously. North Korea would also likely be uncertain as to whether the United States or the PRC would be able to win a decisive victory, regardless of North Korean involvement. Though it may not be possible to deter some posturing or limited aggression by North Korea in such scenarios, there would be an opportunity to raise Pyongyang’s level of caution through integrated deterrence approaches.
• Personnel below the regime leaders’ level in both states could be susceptible to influence to delay or discourage escalation in such scenarios. Their personal interests may sharply diverge from those of their leaders in such extreme circumstances, as the risks of conflict escalation take precedence over fear of punishment for passivity or disobedience. The US and its allies could exploit the tendency of high-level officials in autocratic systems toward delay and confirmation, rather than prompt action.

Biases in US and allied institutions are impeding their understanding of how an East Asian conflict could escalate, and their preparations to manage such escalation. Deep-seated organizational and cognitive biases have obstructed the ability of the United States and its allies to anticipate, deter, and prepare for these two possibilities: simultaneous conflicts with the PRC and North Korea, or limited nuclear attack by either adversary. During the study, members of the research team and many of the expert participants found that such biases have often led to unfounded optimistic assertions, particularly the idea that Beijing or Pyongyang would remain a passive observer while the other fights a conflict that would have profound consequences for the security of both. (For more on the biases at work in the way the United States and its allies think about East Asian security, see Jonathan Corrado’s essay, “Biases blind us to the risk of Chinese military intervention in Korea.”)

• A bias toward overcentralized perception of adversary decision-making has obstructed US consideration of simultaneous conflicts with the PRC and North Korea. Many US personnel who have not closely studied the Pyongyang-Beijing relationship make unsupported assumptions about either the level of coordination between Beijing and Pyongyang or North Korea’s level of responsiveness to PRC direction—driving another assumption, that simultaneous conflicts would only happen by Beijing’s conscious choice. Others assume that the low trust between Beijing and Pyongyang made simultaneous conflicts impossible.
• Mirror imaging and wishful thinking were also common US and allied biases reported by study participants. In particular, some participants reported the widespread belief that the United States and the PRC have a common overriding interest in avoiding a two-front war or nuclear escalation, without considering whether this would hold true if the PRC were losing a war with the United States. Similarly, a frequent response to the idea of a limited North Korean nuclear attack is that North Korea “wouldn’t dare” to use nuclear weapons because its leaders “know it would be the end of their regime,” without considering scenarios in which the regime is already facing imminent destruction.
• What’s known as the “law of the instrument bias” was often identified during the study, as each of the three most relevant US four-star joint commands for these issues has a distinct and separate role. Deterring nuclear attack is the domain of US Strategic Command; deterring PRC aggression is the domain of US Indo-Pacific Command; and North Korean aggression is the domain of Combined Forces Command/US Forces Korea. This makes it difficult, but important, to enable integration across these commands in order to best address security challenges in East Asia. Integration will increase the range of resources available to each command and will thus help commands to view problems from new angles, rather than with a disproportionate focus on their own command’s regional or strategic domain.

How could simultaneous conflicts break out?

Considered separately, the risks to US interests posed by simultaneous conflicts and limited nuclear attacks in East Asia are complex and daunting. Considering them together introduces further complexity. Given the relatively low potential for either the PRC or North Korea to begin aggression with a nuclear attack at the outset of a conflict, this analysis first establishes the potential pathways to simultaneous conflicts with the PRC and North Korea, along with the general scenarios that might result. It then establishes some of the driving and restraining factors for a limited-nuclear-attack decision, and from these derives a summary of conditions wherein simultaneous conflicts would be most likely to place the greatest strain on the potential for limited nuclear attack.

The study found numerous plausible pathways from which aggression by either the PRC or North Korea could result in simultaneous conflicts with the United States in the coming decade, some of which are more likely than others. The study also found some pathways to be implausible. For example, it found that the prospects for a truly “collaborative” decision between Beijing and Pyongyang to initiate joint aggression are remote, even if one assumes that PRC-North Korea relations will have improved a decade from now. Therefore, the following analysis assumes that either Beijing or Pyongyang would be the “first mover” initiating the planning and preparations for such aggression, even in the unlikely scenario that PRC-North Korea relations and trust have improved to the point that some degree of joint planning and preparations take place.

The flow of a conflict initiated by the People’s Republic of China

Beijing has a wide range of potential justifications and motivations for initiating aggression. The scenario that receives the most attention is the potential for a PRC offensive to bring Taiwan under its control, either through a massive amphibious invasion or a coercive campaign using some combination of threats, limited strikes, and isolation of the island. However, there are other plausible scenarios for PRC aggression, including disputes over territorial claims in the South China Sea and the Senkaku Islands. In all of these cases, however, the PRC’s goals appear limited, and the PRC almost certainly seeks—at least at the outset—to achieve a decisive victory without having to resort to nuclear strikes or escalate to a global war with the United States. This is likely to motivate the PRC to limit the geographic scope of its initial aggression, to at least some degree. As a result, the study considered it possible that the PRC could plausibly choose not to initially attack US bases in South Korea, even if it attacks US bases and forces located elsewhere—on Japanese territory, for example. (See Figure 4 for some geographic factors constraining such a PRC approach.) Figure 1 depicts a range of potential pathways for a conflict initiated with a PRC attack on Taiwan to escalate to include North Korea.

The flow of a conflict initiated by North Korea

Pyongyang also has a wide range of possible reasons and incentives for initiating aggression, with its most likely target being South Korea (ROK). For the purposes of this study, a foundational assumption, based on assessments of Pyongyang’s mindset and calculus, is that North Korea’s aggression would be intended to result in a limited conflict—rather than an all-out war to absorb the ROK, which it almost certainly understands it could not win.¹¹ As a result, such a conflict is unlikely to begin with a nuclear attack. To make for a more manageable scope, the study also set aside scenarios of a US- or ROK-initiated “invasion” or intervention in a North Korean collapse.

Figure 2 depicts pathways of how such a conflict could flow, including situations that could serve as triggering conditions for North Korea to conduct a limited nuclear attack. Though focused on the potential for simultaneous conflicts, this graphic also shows that PRC intervention is not necessarily inevitable, and that there is even the possibility of a cooperative US-PRC response. However, the study participants largely assessed such cooperation as unlikely in the context of the expected intensification of US-PRC rivalry in the coming decade.

Will these conflicts go nuclear?

We have no historical record of limited nuclear attacks to inform analysis of what might lead to such an attack—unlike the long track record for nuclear threats, demonstrations, and coercion—so it is appropriate to limit expectations of how confident we can be in such assessments. Similarly, parsing statements on nuclear-weapons policy by Beijing or Pyongyang is likely to reveal more about their current intentions for nuclear signaling than the actual dynamics and calculus for a limited nuclear attack in a conflict up to a decade from now. The wording of Pyongyang’s September 2022 “Law on Policy of Nuclear Forces” establishes explicit justifications for first use of nuclear weapons by North Korea in various scenarios short of all-out nuclear war, but only alludes to the possibility of conducting limited nuclear attacks.¹² The PRC’s potential logic for a limited nuclear attack is even more opaque, given its ostensible “no first use” policy. Despite this current policy, some US scholars argue that Beijing could, in a future war, choose “limited nuclear escalation as a way to force an end to the conflict.”¹³

Lacking concrete evidence of PRC or North Korean calculations for limited nuclear attacks, Figure 3 summarizes a set of potential variables that could either restrain or encourage the adversary considering a limited nuclear attack, modeling the logic of an authoritarian regime considering such options.¹⁴ These considerations are not a definitive “checklist,” but can provide analytic insight on the varying factors that are likely to come into play.

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